Synthesis and Gas Permeability of Chemically Cross‐Linked Polynorbornene Dicarboximides Bearing Fluorinated Moieties

This work reports on the synthesis of a novel bifunctional norbornene dicarboximide monomer (HFDA) based on 4,4′‐(hexafluoroisopropylidene)bis(p‐phenyleneoxy)dianiline and its application as a cross‐linking agent in the ring‐opening metathesis polymerization (ROMP) with N‐3‐trifluoromethylphenyl‐exo,endo‐norbornene‐5,6‐dicarboximide (mCF3) employing the Grubbs 2nd generation catalyst (I) and cis‐1,4‐diacetoxy‐2‐butene as a chain transfer agent (CTA) to yield a series of soluble nonlinear highly branched chains polymers with increasing degree of cross‐linking. A comparative study of gas transport in membranes based on these cross‐linked polynorbornene dicarboximides is performed and the gases studied are hydrogen, oxygen, nitrogen, carbon dioxide, methane, ethylene, and propylene. It is found that cross‐linking increases the gas permeability, leads to the highest separation factor reported to date for the H2/C3H6 mixture in this kind of polymers, and also enhances the CO2 plasticization resistance up to 14 atm upstream pressure. The chemical cross‐linking approach employed in this research is an effective tool to enhance gas transport properties for dense polynorbornene dicarboximide membranes. A novel bifunctional norbornene dicarboximide cross‐linking monomer is synthesized and successfully employed to yield a series of soluble cross‐linked polynorbornene dicarboximides by ring‐opening metathesis polymerization (ROMP). A comparison of the gas transport properties in membranes prepared from the resulting cross‐linked polymers indicates that cross‐linking increases the gas permeability, improves the permselectivity coefficient for separating H2/C3H6 mixture, and enhances the CO2 plasticization resistance.